The present invention relates to an internal combustion engine. The invention is applicable on vehicles, in particularly heavy vehicles, such as e.g. trucks. However, although the invention will mainly be described in relation to a truck, the internal combustion engine is of course also applicable for other type of vehicles, such as cars, industrial construction machines, wheel loaders, etc.
For many years, the demands on internal combustion engines have been steadily increasing and engines are continuously developed to meet the various demands from the market. Reduction of exhaust gases, increasing engine efficiency, i.e. reduced fuel consumption, and lower noise level from the engines are some of the criteria that becomes an important aspect when choosing vehicle engine.
Furthermore, in the field of trucks, there are applicable law directives that have e.g. determined the maximum amount of exhaust gas pollution allowable. Still further, a reduction of the overall cost of the vehicle is important and since the engine constitutes a relatively large portion of the total costs, it is natural that also the costs of engine components are reduced.
In order to meet the described demands, various engine concepts have been developed throughout the years where conventional power cylinders have been combined with e.g. a pre-compression stage and/or an expansion stage.
WO 99/06 682 describes an internal combustion compound engine that aims at providing a relatively light-weighted engine. The internal combustion compound engine disclosed in WO 99/06 682 comprises a first-stage four-stroke combustion unit and a second-stage two-stroke expansion unit. One or more of the first-stage cylinders have pistons driving a first crankshaft and the same number of second-stage expansion cylinders has pistons driving a parallel crankshaft. The second-stage unit can also be arranged as a double-acting cylinder where one side acts as the second expansion stage while the other acts as a pre-compressor or supercharger.
The internal combustion compound engine disclosed in WO 99/06 682 has the advantages of being able to save energy during compression, and thus increasing filet efficiency. The engine may also save and provide reserve energy in the form of compressed air during braking and downhill driving.
Although the internal combustion compound engine described in WO 99/06 682 may increase fuel efficiency as well as saving and providing reserve energy, the engine is still in need of further improvements in terms of e.g. power efficiency and cost.
It is desirable to provide an internal combustion engine having increased power efficiency in relation to prior art engines.
According to a first aspect of the present invention there is provided an internal combustion engine comprising a first set of cylinders comprising: a first two-stroke compression cylinder housing a first compression piston connected to a first crank shaft; an intermediate two-stroke compression cylinder housing an intermediate compression piston, wherein the intermediate two-stroke compression cylinder is configured to receive compressed gas from the first two-stroke compression cylinder; and a first four-stroke combustion cylinder housing a first combustion piston, wherein the first four-stroke combustion cylinder is configured to receive compressed gas from the intermediate two-stroke-compression cylinder; wherein the internal combustion engine further comprises a second set of cylinders comprising: a second two-stroke compression cylinder housing a second compression piston connected to the first crank shaft, wherein the second two-stroke compression cylinder is configured to provide compressed gas to the intermediate two-stroke compression cylinder; and a second four-stroke combustion cylinder housing a second combustion piston, wherein the second four-stroke combustion cylinder is configured to receive compressed gas from the intermediate two-stroke compression cylinder; wherein each one of the intermediate compression piston and the first and second combustion pistons are connected to a second crank shaft, the second crank shaft being configured to rotate with a speed of at least twice the speed of the first crank shaft.
A compression cylinder should in the following and throughout the entire description be interpreted as a cylinder housing a compression piston, where the cylinder is arranged to provide compressed intake gas to another cylinder. In the present invention, the first and second compression cylinders provide compressed gas to the intermediate compression cylinder. The intermediate compression cylinder in turn compresses the gas even further before providing the compressed gas to each of the first and second combustion cylinders. Accordingly, the compression piston compresses gas inside the compression cylinder, which compressed gas thereafter is transferred to the intake of either a further compression cylinder or to a combustion cylinder. The pressure level of the compressed gas is then above atmospheric pressure. The compression cylinders each work in a two-stroke fashion, meaning that when the respective compression piston is in an upper end position of the cylinder, also known as a top dead centre of the cylinder, gas is provided into the cylinder during the downward motion of the compression piston to a lower end position of the compression cylinder, also known as a bottom dead centre of the cylinder. When the compression piston thereafter is in an upward motion towards the upper end position of the cylinder, the gases provided into the cylinder is compressed due to the volume reduction within the cylinder caused by the reciprocating motion of the compression piston. At a desired point in time, the compressed gases are directed out from the compression cylinder and to the intake of the combustion cylinder. A further description of how this is controlled will be given below.
The combustion cylinders are, as described above, four-stroke combustion cylinders, i.e. they have one power stroke and one exhaust stroke for every two revolution of the second crank shaft. When the combustion piston in the respective combustion cylinders are travelling downwards, towards a bottom dead centre of the respective cylinder, the compressed gas from the compression cylinder is forced into the combustion cylinder. When the combustion piston thereafter is travelling upwards toward a top dead centre of the combustion cylinder, the gases in the combustion cylinder are compressed and ignited at a desired point in time. The combustion piston is thereafter, again, traveling downwards towards the bottom dead centre. Finally, when the combustion piston is travelling upwards, the exhaust gases are directed out from the combustion cylinders. Combustion fuel is provided to the combustion cylinders in a fashion known to the person skilled in the art of four-stroke internal combustion engines and will not be discussed further. The invention is also not limited to any particular kind of fuel.
The present invention is based on the insight that by arranging an intermediate “compression cylinder downstream from the first and the second compression cylinder and upstream the first and second combustion cylinders, the compression in each of the compression cylinder can be reduced by still providing gas to the respective combustion cylinders which is sufficiently compressed. Accordingly, an engine having a three-stage compression is provided. Further, by compressing the gas in several stages with intermediate cooling, which is described thither below, the total compression work of the engine is reduced.
An advantage of the invention is that the three-stage compression increases the efficiency of the internal combustion engine, i.e. the power efficiency of the engine may be increased. By utilizing a three-stage compression, the total compression work by the compression cylinders can be reduced in comparison to the use of e.g. a two-stage compression. Furthermore, by using three compression cylinders instead of two, the individual pressure demands on the respective compression cylinders and compression pistons can be reduced in comparison to having two compression stages, where each compression cylinder may need to be able to handle larger pressure. Also the pressure demand on the first and second compression pistons are relatively low such that the cylinders can be designed with low friction coefficients. Furthermore, by providing an intermediate compression stage in the form of the intermediate compression cylinder, it is possible to arrange the first compression piston with a 90 degree crank angle deviation towards the expander. Hereby, the balancing effects of the internal combustion engine are improved. Still further, by positioning the intermediate two-stroke compression piston on the same crank shaft as the first and second four-stroke combustion pistons, it is sufficient with only one compression cylinder since it can alternatingly deliver compressed gas to the first and the second combustion cylinders.
According to an example embodiment, the internal combustion engine may further comprise a first two-stroke expansion cylinder housing a first expansion piston connected to the first crank shaft, the first two-stroke expansion cylinder being configured to receive exhaust gas from the first four-stroke combustion cylinder; and a second two-stroke expansion cylinder housing a second expansion piston connected to the first crank shaft, the second two-stroke expansion cylinder being configured to receive exhaust gas from the second four-stroke combustion cylinder.
An expansion cylinder should in the following and throughout the entire description be interpreted as a cylinder housing an expansion piston, where the cylinder is arranged to receive exhaust gases from the combustion cylinder and thereafter further provide the exhaust gases out from the expansion cylinder. The first and second expansion cylinders work in a two-stroke fashion, meaning that when the respective expansion piston is in an upper end position of the cylinder, exhaust gas from the combustion cylinder is provided into the expansion cylinder during the downward motion of the expansion piston to a lower end position of the expansion cylinder. Hereby, the exhaust gases are expanded due to the increase of the volume within the cylinder in which the expansion piston is reciprocating. When the expansion piston thereafter is in an upward motion towards the upper end position of the cylinder, the exhaust gases provided into the expansion cylinder are directed out from the expansion cylinder, either directly to the atmosphere, or provided to some sort of gas after treatment system, such as e.g. a catalyst or the like.
An advantage is that the power efficiency of the internal combustion engine may be further increased. The expansion cylinder expands the exhaust gases from the respective combustion cylinders and thereby enables for increased thermodynamic efficiency by recovery of chemical energy and heat from the combustion cylinders.
According to an example embodiment, the first compression piston and the second compression piston may be arranged in a 180 degrees crank angle offset in relation to each other, such that the first compression piston is configured to reach an upper end position within the first compression cylinder when the second compression piston reaches a lower end position within the second compression cylinder.
The wording “crank angle offset” should in the following and throughout the description be interpreted as a rotational difference between crank angles for the different pistons, i.e. the crank angle degrees (CAD) between the pistons on the crank shaft. As an example, the four-stroke combustion pistons have a 720 crank angle cycle while the two-stroke compression and expansion pistons each have a 360 crank angle cycle, respectively.
By arranging the compression pistons with a 180 degrees crank angle offset in relation to each other, the intermediate compression piston, which operates at twice the speed of the first and second compression pistons, will receive compressed gas continuously when the intermediate compression piston is in its top dead centre position. More specifically, the intermediate compression piston will be positioned in its top dead centre position when the first compression is positioned in a mid portion of the first compression cylinder.
According to an example embodiment, the intermediate compression piston and the first combustion piston may be arranged in a 180 degrees crank angle offset in relation to each other, such that the intermediate compression piston is configured to reach an upper end position within the intermediate compression cylinder when the first combustion piston reaches a lower end position within the first combustion cylinder.
Further, the intermediate compression piston may have approximately the same size as the first and second combustion pistons, respectively. Hereby, first order-unbalances arising from the first and second combustion pistons can be at least partially extinguished by the motion and inertia forces of the intermediate compression piston in collaboration with the respective combustion pistons.
According to an example embodiment, the first combustion piston and the second combustion piston may be positioned to reach an upper end position within the respective combustion cylinders approximately simultaneously and in such a way that the first combustion piston is configured to be ignited at an upper end position within the first combustion cylinder when the second combustion piston is in an upper end position of the second combustion cylinder for initiation of intake of fuel therein.
An advantage of providing the combustion pistons in the above manner, i.e. with approximately 360 degrees offset in relation to each other is that a combustion stroke will occur for every revolution of the second crank shaft, thereby providing a continuous engine torque. The internal combustion engine is off course working well with minor deviation from the 360 degrees offset, which should not be construed as an absolute value of the internal relationship between the first and second combustion pistons. Also, the configuration of the cylinders is arranged in such a way that compressed as from the intermediate compression cylinder can alternatingly be provided to either the first or the second combustion cylinders.
According to an example embodiment, the first expansion piston and the second expansion piston may be arranged in a 180 degrees crank angle offset in relation to each other, such that the first expansion piston is configured to reach an upper end position within the first expansion cylinder when the second expansion piston reaches a lower end position within the second expansion cylinder.
The motion of the expansion pistons in the expansion cylinders are thus synchronized with the motion of the respective combustion cylinders.
According to an example embodiment, the first expansion piston and the first compression piston may be arranged in a 90 degrees crank angle offset in relation to each other, such that the first compression piston is configured to reach an upper end position within the first compression cylinder when the first expansion piston is located in a mid-portion within the first expansion cylinder. Hereby, the balancing effects of the internal combustion engine are improved due to the mutual relationship between the motion of the masses for the different pistons and their respective connecting rods. In more detail, by arranging two cylinders in a 90 degree V-shape, wherein pistons sharing the same pin on the crank shaft, it is possible to fully balance first order unbalances from the piston masses with balance weights on the crank shaft.
According to an example embodiment, a first and a second compression con rod may be connected to the first and second compression piston, respectively, and a first and a second expansion con rod may be connected to the first and second expansion piston, respectively, wherein the first compression con rod and the first expansion con rod is connected to a first crank pin of the first crank shaft, and wherein the second compression con rod and the second expansion con rod is connected to a second crank pin of the first crank shaft. Hereby, further control of the mutual motion pattern of the cylinders is provided.
According to an example embodiment, the first and second compression cylinders may be positioned in parallel in relation to each other and the first and second expansion cylinders may be positioned in parallel in relation to each other, wherein the compression cylinders and the expansion cylinders are arranged in a V-shaped configuration in relation to each other.
According to an example embodiment, each of the cylinders may comprise valved inlet ports and valved outlet port for controlling fluid transportation into and out from the respective cylinders.
Hereby, it is possible to control the fluid transportation by opening and closing the valved outlet ports at suitable intervals. For example, the valved outlet ports of the first compression cylinder may be controlled to be in an opened state when the pressure in the first compression cylinder has reached a predetermined pressure limit. Different types of valved ports are well known to the skilled person and will not be described further. The valved ports can be controlled by means of an already available control unit of the engine or vehicle onto which the engine is to be mounted.
According to an example embodiment, each one of the first and second compression cylinders may be arranged in fluid communication with the intermediate compression cylinder by means of a respective first and second passageway. According to an example embodiment, the intermediate compression cylinder may be in fluid communication with the first and second combustion cylinders by means of a respective third and fourth passageway. According to an example embodiment, the first combustion cylinder may be in fluid communication with the first expansion cylinder by means of a fifth passageway. According to an example embodiment, the second combustion cylinder may be in fluid communication with the second expansion cylinder by means of a sixth passageway. Hereby, well defined passages are provided between the cylinders for transportation of gas and/or exhaust gas to/from the respective cylinders.
According to an example embodiment, the first, second, third and/or fourth passageways may be provided with cooling means for cooling the fluid passing there through. Hereby, the power consumption of the internal combustion engine can be reduced since the pressure level of the cooling means can be increased in comparison to previously known engines. An overall lower compression work is provided which improves engine efficiency and durability. A colder internal combustion engine is also provided. The cooling means may e.g. be a heat exchanger or the like.
According to an example embodiment, the first compression cylinder and the second compression cylinder may be one and the same compression cylinder, and the first compression piston and the second compression piston may be one and the same compression piston, wherein the compression cylinder is configured to provide a first compression when the compression piston reaches an upper position within the compression cylinder, and to provide a second compression when the compression piston reaches a lower position within the compression cylinder.
Hereby, instead of using two separate compression cylinders, one compression cylinder, housing a piston that compress gas in both its reciprocating directions, may be sufficient. An advantage is that the overall size of the engine can be reduced and the engine may hence be more cost efficient since less material for the engine is needed. Accordingly, a dual-acting compression cylinder is provided.
According to a second aspect of the present invention, there is provided a vehicle comprising an internal combustion engine according to any one of the above described example embodiments.
Effects and features of this second aspect are largely analogous to those describe above in relation to the first aspect of the present invention.
Further features of and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.